202 Love and Smeal : 



theoretical result that the two values should be in the inverse 

 ratio of the latent heats of ice and water. Kegnault noticed 

 that the ice exerts a hygroscopic effect in very humid air, caus- 

 ing condensation on its surface, and other observers since his 

 time have confirmed this. To allow for it, suggestions have 

 been made for a correction of the observed value of either 

 t or t'. Ekholm proceeds a step further by stating that the 

 hygroscopic action of the ice is accompanied by a similar action 

 of the material on which the ice is deposited, this latter action 

 therefore varying with the nature of the material employed. 

 He performed some experiments in which two wet-bulb ther- 

 mometers coated with different stuffs were enclosed with a dry 

 bulb thermometer in an air-tight vessel ; sufficient water was 

 poured in to form a layer on the bottom, and the whole main- 

 tained at a temperature below zero. The wet-bulbs, being 

 coated with ice, and in contact with air nearly or completely 

 saturated with water-vapour, received heat by condensation of 

 vapour, and indicated higher temperatures than the dry bulb. 

 This, of course, is due to the fact, unknown to Regnault, that 

 the vapour-pressure of ice is less than that of water at the 

 same temperature. The results of the observations are given 

 as follows : — 



Dry Bulb. Wet Bulb. 



Cotton. Wool. 



- 4.05 - - 3.83 - —3.85 



- 4.0 - - 3.88 - - 3.85 



- 4.0 - - 3.88 - - 3.85 



- 3.55 - - 3.20 - - 3.27 



